A. Field of the Invention
The present invention relates to wide angle lenses, and more particularly, to high resolution 180.degree. angle projection lenses.
B. Description of the Prior Art
Although wide angle lenses are known, difficulties are encountered when attempts are made to build so-called fisheye lenses having a 180.degree. projection angle while maintaining high resolution, high lens speed and a sufficiently long back focal length. Thus, conventional wide angle fisheye lenses typically are not suitable for projecting motion pictures, since the short back focal length requires the lens to be placed so close to the film plane that it interferes with the shutter and film advancing mechanism. Furthermore, the lens speed must be high to permit the lens to intercept enough light from the light source within the projector to generate a sufficiently bright projected image. The high speed required to project a bright image tends to reduce lens resolution unless steps are taken to compensate for the resolution loss. Such steps tend to make the lens more complex and costly.